DE19633156A1 - Device and method for controlling an internal combustion engine - Google Patents

Description

State of the art

The invention relates to a method and a device for controlling an internal combustion engine according to the General terms of the independent claims.

Such a method and such an apparatus are out DE-OS 31 18 425 (US 4,426,981) is known. There will be one Described device that determines the amount of fuel, which are fed to the combustion chambers of a diesel engine becomes. For this purpose, a sensor detects the fuel pressure in one so-called element space and provides a corresponding signal ready. The injection quantity is dependent on this signal and / or the start of injection and other sizes such as controlled exhaust gas recirculation, for example.

The course of the pressure over time or over the angular position of the crankshaft or camshaft is subject strong fluctuations. Taking temperature into account the fuel is not with this device intended. The temperature and composition of the  Have a significant impact on the fuel Power output, pollutant emissions and Noise development of the internal combustion engine.

Facilities are known in which the Fuel temperature is taken into account in that a Temperature sensor is provided which the temperature of the Fuel detected. There is an additional one Temperature sensor required. Especially with newer ones Metering systems, such as common rail systems or pump-nozzle systems, the temperature sensor must be switched on appropriate place.

The object of the invention is fuel properties, such as for example the temperature and / or the compressibility of the fuel without detecting additional sensors.

Advantages of the invention

With the procedure according to the invention it is possible to Fuel properties, especially the temperature of the Fuel, in the fuel metering without additional Sensors to consider.

Advantageous and expedient configurations and Further developments of the invention are in the subclaims featured.

drawing

The invention is described below with reference to the drawing illustrated embodiments explained. Show it

Fig. 1 is a block diagram of the device according to the invention, Fig. 2, 3 and FIG. 4 show various signals plotted against time, Fig. 5 is a flowchart and Fig. 6 is a characteristic diagram.

Description of the embodiment

The procedure according to the invention is described below on Example of a diesel engine described.

Fig. 1 shows in a rough overview of an internal combustion engine with self-ignition, along with their significant electronic control devices. 10 denotes the internal combustion engine, to which an air intake pipe 11 leads and an exhaust pipe 12 leads away. An exhaust gas recirculation line is designated by 13 . The proportion of fresh air and exhaust gas fed to the internal combustion engine 10 is set by means of a mixing flap 14 , which receives its control signal via an exhaust gas recirculation control stage 15 .

The internal combustion engine 10 is supplied with fuel from a tank 18 via a fuel pump 17 . In the embodiment shown, the pump itself has two control inputs 19 and 20 for the fuel quantity and the start of injection. Correspondingly, these two control inputs 19 and 20 are connected to the signal outputs 21 and 22 of a quantity control stage 23 and an injection start control stage 24 .

The exemplary embodiment shown is a distributor pump in which a volume control and a Spray start control are provided. With newer ones solenoid valve controlled systems is an electrical one controllable valve provided that both the start of injection controls the injection quantity as well. In this case only one control line is provided, which is the valve  controls. The quantity tax level and the Spray start control stage then together form the signal for Actuation of the valve.

For the exemplary embodiment, the speed, the accelerator pedal position and a pressure signal relating to the fuel to be injected are essential as input variables for the entire device. Accordingly, the output signal of a speed sensor 25 reaches the corresponding inputs of the exhaust gas recirculation control stage 15, the quantity control stage and the injection start control stage ( 23 and 24 ). An accelerator pedal position signal comes from a corresponding sensor 26 and is switched to the fuel quantity control stage 23 .

A pressure sensor 27 for detecting the fuel pressure outputs its output signal to a signal processing stage 29 . It has two outlets 30 and 31 for the amount of fuel injected and the start of injection. Correspondingly, these outputs 30 and 31 are connected to the exhaust gas recirculation control stage 15 , the fuel quantity control stage 23 and the injection start control stage 24 . All three control stages 15 , 23 and 24 also have additional inputs 32 , 33 and 34 , via which the individual values can also be influenced. Such a device is described for example in DE-OS 31 18 425 (US 4,426,981).

In conventional systems, the Pressure curve over time t only the start of injection, the end of injection and thus the injected Determined fuel quantity. According to the invention, it was recognized that starting from the course of the pressure P in the element space Fuel pump on other fuel properties, such as  especially the temperature of the fuel, closed can be. This requires that the course of the Pressure P over time t when pressure builds up and / or when Pressure reduction is observed.

In conventional fuel pumps, especially distributor and Inline pumps, a pressure sensor is required, which the Pressure P detected in the element space of the pump. With newer ones Systems, such as pump-nozzle or Pump line nozzle systems must also the pressure in Element space can be recorded during compression. With common Rail systems must have the pressure in the high pressure pump and / or in the rail during compaction.

Starting from the pressure curve, variables are determined that characterize the fuel properties. These are in particular the temperature of the fuel, the viscosity, the density, the speed of sound and the modulus of elasticity of the fuel. These quantities are then used by the quantity control stage 21 , the start of injection control stage 22 , the exhaust gas recirculation control stage 15 and, if appropriate, in further control stages in fuel metering or in other controls, such as exhaust gas recirculation.

It is advantageous with this procedure that none additional temperature sensor to record the Fuel temperature is required. A corresponding one Temperature sensor can therefore be saved. It is only a fuel pressure sensor required for other measurement tasks are needed.

By recording the pressure curve over time in the High pressure area of the injection system becomes information about temperature or equation of state of the  Won fuel. These are especially for the Hydraulic fuel quality.

Various signals are plotted over time in FIG . The course of the pressure P is plotted over time in FIG. 2a. A first signal S1 is plotted in FIG. 2b and a second signal S2 is plotted over time in FIG. 2c.

In Fig. 2a, two pressure profiles, which are designated I and II, are plotted over time. These profiles are only examples and, depending on the configuration of the fuel pump, can have other profiles. I is an exemplary value for a lower temperature and II is a curve for a higher temperature. At low temperatures, the pressure rises faster and drops correspondingly faster. At high temperatures, the pressure rises more slowly and falls more slowly.

Furthermore, different pressure thresholds P1, P2, P3 and P4 are shown in FIG. 2a. In conventional systems, when the pressure threshold P1 is exceeded, the start of injection is detected and when the pressure threshold P4 is undershot at the end of injection.

The sub-figure 2b shows the signal S1, which at conventional systems when the Threshold P1 and falling below the threshold value P4 is formed. The pressure exceeds at low temperature the first threshold value P1 at time t (P1). With this At this point in time, the signal S1 drops from its high to one low level. This drop in signal S1 is caused by the Control recognized as start of spraying. At time t (P4) pressure P drops below its fourth threshold value P4. To At this time t (P4) the signal S1 rises to its high  Level on. The time period between t (P1) and t (P4) is called Injection duration denotes and determines the injected Amount of fuel.

At higher temperatures, the pressure P only exceeds the threshold value P1 at a later time t ′ (P1). It falls below the threshold value P4 only at a later time t ′ (P4). Accordingly, the signal S1 drops only at time t '(P1) and rises to its high level at time t' (P4). This is indicated by a dashed line in FIG. 2b.

In the illustrated embodiment shifts at higher fuel temperatures Start of injection and end of injection at later Times.

Since the start of injection and the end of injection of depends on various operating parameters, this can Shift in start of injection and End of injection signal not for temperature measurement be used. Hence more Pressure thresholds P2 and P3 introduced. These lie preferably higher than the pressure thresholds P1 and P4. The Pressure threshold P2 rises and pressure threshold P3 lies in the drop in the pressure signal.

When the pressure threshold P2 is exceeded, the signal S2 drops to its low value and rises to its high value when the pressure threshold P3 is undershot. Corresponding to FIG. 2b, the course of the signal S2 is drawn with a solid line at low temperature and with a dashed line at high temperature in FIG. 2c. At high temperature, the pressure rises above the threshold value P2 at time t (P2) and falls below the threshold value P3 at time t (P3).

Can be used to record the fuel properties different sizes can be evaluated. At a first Embodiment are the angle or Time difference between two defined pressure levels in the Range of increasing pressure measured. This means it for example, the distance between the time t (P1) and time t (P2) or t ′ (P1) and t ′ (P2) evaluated. That said, it will be the distance between that Exceeding the first threshold P1 and the second Threshold P2 taken into account. At low temperatures the time difference Δt between the time t (P2) and the Time t (P1) less than at high temperature.

Accordingly, the distances between two defined pressure levels in the area of the falling pressure be measured. This means it will be the distance between falling below the third threshold P3 and the fourth Threshold P4 evaluated. At low temperatures it is Time difference Δt * between the time t (P4) and the Time t (P3) less than at high temperature.

Furthermore, the value of the maximum pressure can also be measured will. Accordingly, the location of the maximum pressure be taken into account. As a rule, the maximum pressure the lower the temperature, the greater. Of the functional relationship depends on the type of pump and must be determined as part of the application.

Another embodiment provides that the pressure curve through integration or differentiation over time in a defined area is detected. This means it is the slope of the pressure at a defined point in time  detected. The lower the temperature, the higher it is Amounts of the gradients.

A particularly advantageous embodiment results if with an additional sensor the temperature is measured and additional information based on the pressure curve on the fuel quality and the condition of the Injection hydraulics regarding leak rates is obtained. At given temperature is the slope of the pressure change a function of fuel compressibility. A high Compressibility requires a small slope. These measures can be used individually or in combination Determination of the fuel quality can be used.

The pressure curve over the time t or over the Angular position of the cam and / or the crankshaft is evaluated. The times or the corresponding angular positions of the crank and / or Camshaft can be used.

Sensors that have a signal can be used as the sensor Provide that shows the entire history of the print. It is particularly advantageous if pressure sensors are used only when threshold values are exceeded Provide changed output signal. Such sensors are particularly inexpensive.

For example, sensors can be used that provide a signal shown in FIG. 2b. When a first threshold P1 is exceeded and a fourth threshold P4 is undershot, the output signal of the pressure sensor changes from a first to a second value. The first pressure threshold is usually in the range of 50 bar and the fourth pressure threshold P4 in the range of 75 bar.

According to the invention, two more Pressure thresholds are defined and reached by the sensor output as a digital signal. The pressure sensor is also used a second digital output, on which the signal S2 is present. The disadvantage of this procedure is that a second output for the sensor must be provided.

In Fig. 3, an embodiment is shown, is necessary in which only an output of the pressure sensor.

In Fig. 3a, the course of the pressure is plotted against time t at different temperatures. Corresponding pressure thresholds as in Fig. 2a are designated accordingly in Fig. 3a. The pressure sensor is designed such that it changes from its high to its low level when the first threshold value P1 is exceeded and from its low to its high level when the second threshold P2 is exceeded. If the pressure drops below the third threshold P3, it changes to its low level and to the high level if the pressure drops below the fourth pressure P4. The levels of the signals can also be opposite.

In Fig. 3b the output signal S is shown of the pressure sensor at a high temperature of the fuel. At time t '(P1), the pressure (II) exceeds the first threshold P1 and the output signal S of the pressure sensor drops. At time t '(P2), the pressure exceeds the second threshold value P2 and the output signal S of the pressure sensor rises to its high level. At time t '(P3), the pressure falls below the threshold value P3 and the output signal S of the pressure sensor drops to its low level. At time t '(P4) the pressure falls below the fourth threshold P4 and the output signal S of the pressure sensor rises again to its high level.

In Fig. 3c, the signal S is shown for lower temperatures. At time t (P1) the pressure (I) exceeds the first threshold P1 and the output signal S of the pressure sensor drops. At time t (P2), the pressure exceeds the second threshold value P2 and the output signal S of the pressure sensor rises to its high level. At time t (P3), the pressure falls below the threshold value P3 and the output signal S of the pressure sensor drops to its low level. At time t (P4), the pressure falls below the fourth threshold value P4 and the output signal S of the pressure sensor rises again to its high level.

The evaluation is carried out in the same way as in the embodiment of FIG. 2. The only difference with the two embodiments is that in the embodiment according to FIG. 3 only one output has to be provided for the pressure sensor, and in FIG. 2 two outputs have to be provided. Falling and rising edges of the output signal S or the output signals S1 and S2 define the times t (P1) to t (P4).

For a pressure sensor that provides a continuous signal for the pressure curve provides a check accordingly trained institution when the thresholds exceeded or fallen below. The time t (P1) to t (P4) are then used to determine the temperature evaluated. When there is a continuous signal also an evaluation of the differentiated and / or integrated pressure signal possible.  

In the illustrated embodiments, all are Threshold values differ. It is also advantageous if the threshold values P1 and P4 and the threshold values P2 and P3 can be chosen equally.

The pressure curve shown in Fig. 2 and Fig. 3 is obtained only in systems where a continuous pressure build-up and pressure reduction takes place. In the case of so-called common rail systems in particular, the pressure is built up to a very high value and then generally remains at this value during operation of the internal combustion engine. In such systems, only an evaluation of the pressure increase during pressure build-up is useful.

In FIG. 4 the curve of the pressure P over the time t plotted for different temperatures. The course at a low temperature or with a fuel with low compressibility is marked with I in FIG. 4. The pressure curve at high temperature or with high compressibility is marked with II. At low temperatures, the pressure rises very quickly over time. This means that the pressure signal has a large slope. At high temperatures the pressure rises more slowly, it has a lower slope.

With P1 and P2 there are two threshold values for the pressure designated. At time t (P1) the pressure exceeds first threshold P1 and at time t (P2) Threshold value P2 at low temperature. At high temperature the pressure at time t ′ (P1) exceeds the first Threshold P1 and the second at time t ′ (P2) Threshold P2. By evaluating the distance between the Times of exceeding the first and second  Threshold values, i. H. between times t (P1) and t (P2) can be concluded on the temperature.

A possible procedure for evaluating the pressure curve is shown as an example in FIG. 5 as a flow chart. The program starts at 500 each time the engine is restarted. In the subsequent step 510, a time counter t is increased by a predetermined value Δ. The subsequent query 520 checks whether the pressure P is greater than the threshold value P1. If this is not the case, step 510 follows again. If the pressure P is greater than or equal to the threshold value P1, the time t (P1) is set in step 530 with the value of the time counter t.

Then in step 540, the time counter t is again increases the predetermined value Δ. The subsequent query 550 checks whether the pressure P is greater than the second Threshold P2 is. If this is not the case, the Time counter increased again in step 540. Is the pressure P greater than or equal to the threshold value P2, so in step 560 the value t (P2) is set with the content of the time counter t.

The subsequent query 570 checks whether the difference between the times t (P2) and t (P1) is greater than a threshold value SW. If this is the case, then an error is recognized in step 580 because the pressure increase was too slow. If the difference between the times t (P2) and t (P1) is less than a threshold value SW, the temperature T or the compressibility of the fuel is determined based on this difference in step 590. This is preferably done by storing the relationship between the difference Δt = t (P2) -t (P1) and the temperature T in a map or in a characteristic curve. The value T for the temperature of the fuel or for the compressibility of the fuel is preferably read from this map.

Alternatively, it can also be provided that the Increase in fuel by differentiating the Pressure curve over time is obtained instead of Size Δt immediately increases the slope of the pressure signal predetermined time is evaluated.

In FIG. 6, a characteristic diagram is illustrated that shows the relationship between the difference .DELTA.t and the temperature T of the fuel. The relationship between the difference Δt and the temperature of the fuel is almost linear. With increasing temperature, the distance Δt between the exceeding of the first and the second pressure threshold increases. At a standard temperature at which the characteristic maps are usually applied, the difference takes on the value Δt0. In the embodiment shown, this temperature assumes the value 45 °. Based on this temperature value and the measured value for Δt, the temperature is read out from the characteristic diagram and / or calculated.

An increased accuracy results when the map values additionally depending on the speed N of Internal combustion engine and the amount of fuel injected and / or a corresponding size.

The problem is that with different pumps and / or fuel types, different values for Δt result at the standard temperature. Such a map is shown in dashed lines in FIG. 6. To compensate for this effect, the value for Δt is learned at the standard temperature. For this purpose, the value Δt is measured in operating states in which the temperature is known and / or can be measured with other sensors, such as the cooling water temperature sensor. The difference from the value Δt0, which should result at the standard temperature of 45 °, is saved. This stored value is marked with a double arrow in FIG. 6. The current temperature is calculated on the basis of this adapted value, the measured value Δt and the known relationship between the difference Δt and the temperature T, that is to say the slope of the straight line.

If a temperature sensor is provided, the Detects fuel temperature, based on the value Δt and the measured temperature on the type of fuel getting closed.

It is particularly advantageous if the value Δt certain temperature value to check the Temperature sensor is used. They give way Temperature values by more than an allowable value from each other, the temperature sensor is defective recognized.

It is particularly advantageous that the pressure sensor signals for Control, such as a signal related to the Start of funding and a signal regarding the funding period, provides and additionally provides a signal, that corresponds to the temperature of the fuel.

Firstly, a separate fuel temperature sensor be saved, on the other hand results in the Using an additional temperature sensor is an increased Failure safety in the event of a defect and / or failure of the Temperature sensor. If there is a temperature sensor, you can in a simple manner the characteristics and / or the variety of the Fuel can be determined.  

The signals determined in this way, in particular the Fuel temperature and / or the fuel properties are used to control and / or regulate different sizes the internal combustion engine used. These sizes will be in particular for controlling and / or regulating the Injection quantity, the start of injection, the exhaust gas recirculation rate and / or other sizes used.

Claims (10)

1. A method for controlling an internal combustion engine, in particular a diesel internal combustion engine, wherein a pressure signal is determined and the fuel metering is controlled as a function of this pressure signal, the pressure signal depending on the course of the fuel pressure over time and / or over the angular position of a shaft, characterized in that based on the pressure signal, a signal is provided that characterizes the fuel properties. 2. The method according to claim 1, characterized in that a signal is provided based on the pressure signal that characterizes the temperature of the fuel. 3. The method according to any one of the preceding claims, characterized in that a first and a second pressure threshold in the area of increasing pressure and / or can be specified in the area of the falling pressure. 4. The method according to any one of claims 2 to 4, characterized characterized in that the formation of the signal Angular difference and / or the time difference between the Reaching the first and second pressure threshold be evaluated.   5. The method according to any one of claims 1 or 2, characterized characterized in that the value to form the signal and / or the position of the maximum pressure can be evaluated. 6. The method according to any one of claims 1 or 2, characterized characterized in that the course of the Pressure signal differentiated and / or integrated. 7. The method according to any one of the preceding claims, characterized characterized in that starting from the pressure signal and a Temperature signal is provided a signal that the Fuel compressibility and / or fuel quality characterized. 8. The method according to any one of the preceding claims, characterized characterized in that the signal for monitoring a Temperature sensor is used. 9. The method according to any one of the preceding claims, characterized characterized in that the determined signal for control and / or regulation of different sizes of Internal combustion engine can be used. 10. Device for controlling an internal combustion engine, in particular a diesel internal combustion engine, with means which determine a pressure signal and the fuel metering control depending on this pressure signal, which Pressure signal from the course of the fuel pressure over time and / or depends on the angular position of a shaft, characterized in that means are provided which provide a signal based on the pressure signal that characterized the fuel properties.